Process for preparing 1,3-propanediol

ABSTRACT

1,3-propanediol is prepared in a process comprising the steps of: 
     contacting ethylene oxide with carbon monoxide and hydrogen in an essentially non-water-miscible solvent in the presence of an effective amount of a non-phosphine-ligated cobalt catalyst and an effective amount of a lipophilic phenol at a temperature within the range of about 50° to about 100° C. and a pressure within the range of about 500 to about 5000 psig, under reaction conditions effective to produce an intermediate product mixture comprising less than about 15 wt % 3-hydroxypropanal; 
     adding an aqueous liquid to said intermediate product mixture and extracting into said aqueous liquid at a temperature less than about 100° C. a major portion of the 3-hydroxypropanal so as to provide an aqueous phase comprising 3-hydroxypropanal in greater concentration than the concentration of 3-hydroxypropanal in said intermediate product mixture and an organic phase comprising at least a portion of the cobalt catalyst or a cobalt-containing derivative thereof and at least a portion of the lipophilic phenol; 
     contacting the aqueous phase comprising 3-hydroxypropanal with hydrogen in the presence of a hydrogenation catalyst at a pressure of at least about 100 psig and a temperature during at least a portion of the hydrogenation step of at least 40° C. to provide a hydrogenation product mixture comprising 1,3-propanediol.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of 1,3-propanediol. In oneaspect, the invention relates to a cobalt-catalyzed process formanufacturing 1,3-propanediol in high yields without the use of aphosphine ligand for the cobalt catalyst.

1,3-propanediol (PDO) is an intermediate in the production of polyestersfor fibers and films. It is known to prepare PDO in a two-step processinvolving (1) the cobalt-catalyzed hydroformylation (reaction withsynthesis gas, H₂ /CO) of ethylene oxide to intermediate3-hydroxypropanal (HPA) and (2) subsequent hydrogenation of the HPA toPDO. The initial hydroformylation process can be carried out attemperatures greater than 100° C. and at high syngas pressures toachieve practical reaction rates. The resulting product mixture is,however, rather unselective for HPA.

In an alternate synthesis method, the cobalt catalyst is used incombination with a phosphine ligand to prepare HPA with greaterselectivity and at lower temperature and pressure. However, the use of aphosphine ligand adds to the cost of the catalyst and increases thecomplexity of catalyst recycle.

It would be desirable to prepare HPA in a low temperature, selectiveprocess which did not require the use of a phosphine ligand with thecobalt catalyst.

It is therefore an object of the invention to provide an economicalprocess for the preparation of 1,3-propanediol which does not requirethe use of a phosphine-ligated catalyst for preparation of the HPAintermediate. It is a further object of one embodiment of the inventionto provide a process for the preparation of 1,3-propanediol in whichessentially all the cobalt hydroformylation catalyst can be convenientlyrecycled.

SUMMARY OF THE INVENTION

According to the invention, 1,3-propanediol is prepared in a processcomprising the steps of:

(a) contacting ethylene oxide with carbon monoxide and hydrogen in anessentially non-water-miscible solvent in the presence of an effectiveamount of a non-phosphine-ligated cobalt catalyst and an effectiveamount of a phenolic compound promoter at a temperature within the rangeof about 50° to about 100° C. and a pressure within the range of about500 to about 5000 psig, under reaction conditions effective to producean intermediate product mixture comprising less than about 15 wt %3-hydroxypropanal;

(b) adding an aqueous liquid to said intermediate product mixture andextracting into said aqueous liquid at a temperature less than about100° C. a major portion of the 3-hydroxypropanal so as to provide anaqueous phase comprising 3-hydroxypropanal in greater concentration thanthe concentration of 3-hydroxypropanal in said intermediate productmixture, and an organic phase comprising at least a portion of thecobalt catalyst or a cobalt-containing derivative thereof and at least aportion of the lipophilic phenolic compound;

(c) separating the aqueous phase from the organic phase;

(d) contacting the aqueous phase comprising 3-hydroxypropanal withhydrogen in the presence of a hydrogenation catalyst at a pressure of atleast about 100 psig and a temperature during at least a portion of thehydrogenation step of at least 40° C. to provide a hydrogenation productmixture comprising 1,3-propanediol;

(e) recovering 1,3-propanediol from said hydrogenation product mixture;and

(f) returning at least a portion of the organic phase comprising cobaltcatalyst and lipophilic phenolic compound to the process of step (a).

The process enables the production of 1,3-propanediol in high yields andselectivity without the use of a phosphine ligated cobalt catalyst inthe hydroformylation step. The process also enables the recovery andrecycle of essentially all the cobalt catalyst.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic flow diagram of one embodiment of the invention1,3-propanediol preparation process.

DETAILED DESCRIPTION OF THE INVENTION

The invention 1,3-propanediol preparation process can be convenientlydescribed by reference to FIG. 1. Separate or combined streams ofethylene oxide 1, carbon monoxide and hydrogen 2 are charged tohydroformylation vessel 3, which can be a pressure reaction vessel suchas a bubble column or agitated tank, operated batchwise or in acontinuous manner. The feed streams are contacted in the presence of anon-phosphine-ligated cobalt catalyst, i.e., a cobalt carbonylcomposition which has not been prereacted with a phosphine ligand. Thehydrogen and carbon monoxide will generally be introduced into thereaction vessel in a molar ratio within the range of about 1:2 to about8:1, preferably about 1.5:1 to about 5:1.

The reaction is carried out under conditions effective to produce ahydroformylation reaction product mixture containing a major portion of3-hydroxypropanal (HPA) and a minor portion of acetaldehyde, whilemaintaining the level of 3-hydroxypropanal in the reaction mixture atless than 15 wt %, preferably within the range of about 5 to about 10 wt%. (To provide for solvents having different densities, the desiredconcentration of HPA in the reaction mixture can be expressed inmolarity, i.e., less than 1.5M, preferably within the range of about 0.5to about 1M.) Generally, the hydroformylation reaction is carried out atelevated temperature less than 100° C., preferably about 60° to about90° C. most preferably about 75° to about 85° C., and at a pressurewithin the range of about 500 to about 5000 psig, preferably (forprocess economics) about 1000 to about 3500 psig, with higher pressuresgenerally imparting greater selectivity. The concentration of3-hydroxypropanal in the intermediate product mixture can be controlledby regulation of process conditions such as ethylene oxideconcentration, catalyst concentration, reaction temperature andresidence time. In general, relatively low reaction temperatures (belowabout 90° C.) and relatively short residence times (about 20 minutes toabout 1 hour) are preferred. In the practice of the invention it ispossible to achieve HPA yields (based on ethylene oxide conversion) ofgreater than 80%, with formation of more than 7 wt % HPA in the dilutehydroformylation product mixture, at rates greater than 30 h⁻¹.(Catalytic rates are referred to herein in terms of "turnover frequency"or "TOF" and are expressed in units of moles per mole of cobalt perhour, or h⁻¹.) Reported rates are based on the observation that, beforea majority of the ethylene oxide is converted, the reaction isessentially zero-order in ethylene oxide concentration and proportionalto cobalt concentration.

The hydroformylation reaction is carried out in a liquid solvent inertto the reactants. By "inert" is meant that the solvent is not consumedduring the course of the reaction. In general, ideal solvents for thephosphine ligand-free process will solubilize carbon monoxide, will beessentially non-water-miscible and will exhibit low to moderate polaritysuch that the 3-hydroxypropanal intermediate will be solubilized to thedesired concentration of at least about 5 wt % under hydroformylationconditions, while significant solvent will remain as a separate phaseupon water extraction. By "essentially non-water-miscible" is meant thatthe solvent has a solubility in water at 25° C. of less than 25 wt % soas to form a separate hydrocarbon-rich phase upon water extraction ofHPA from the hydroformylation reaction mixture. Preferably thissolubility is less than about 10%, most preferably less than about 5 wt%. The solubilization of carbon monoxide in the selected solvent willgenerally be greater than 0.15 v/v (1 atm, 25° C.) preferably greaterthan 0.25 v/v, expressed in terms of Ostwald coefficients.

The preferred class of solvents are alcohols and ethers which can bedescribed according to the formula

    R.sub.2 --O--R.sub.1                                       (1)

in which R₁ is hydrogen or Cue linear, branched, cyclic or aromatichydrocarbyl and R₂ is a C₁₋₂₀ linear, branched, cyclic or aromatic C₁₋₂₀hydrocarbyl, alkoxy or mono- or polyalkylene oxide. The most preferredhydroformylation solvents can be described by the formula ##STR1## inwhich R₁ is hydrogen or C₁₋₈ hydrocarbyl and R₃, R₄ and R₅ areindependently selected from C₁₋₈ hydrocarbyl, alkoxy and alkylene oxide.Such ethers include, for example, methyl-t-butyl ether, ethyl-t-butylether, ethoxyethyl ether, phenylisobutyl ether, diphenyl ether, diethylether, and diisopropyl ether. Blends of solvents such astetrahydrofuran/toluene, tetrahydrofuran/heptane andt-butylalcohol/hexane can also be used to achieve the desired solventproperties. The currently preferred solvent, because of the high yieldsof HPA which can be achieved under moderate reaction conditions, ismethyl-t-butyl ether.

The catalyst is a non-phosphine-ligated cobalt carbonyl compound.Although phosphine-ligated catalysts are active for hydroformylationreactions, the invention process is designed to achieve good yield andselectivity without the additional expense of the ligand. The cobaltcatalyst can be supplied to the hydroformylation reactor in essentiallyany form including metal, supported metal, Raney-cobalt, hydroxide,oxide, carbonate, sulfate, acetylacetonate, salt of a carboxylic acid,or as an aqueous cobalt salt solution, for example. It may be supplieddirectly as a cobalt carbonyl such as dicobaltoctacarbonyl or cobalthydridocarbonyl. If not supplied in the latter forms, operatingconditions can be adjusted such that cobalt carbonyls are formed in situvia reaction with H₂ and CO, as described in J. Falbe, "Carbon Monoxidein Organic Synthesis," Springer-Verlag, N.Y. (1970) In general, catalystformation conditions will include a temperature of at least 50° C. and acarbon monoxide partial pressure of at least about 100 psig. For morerapid reaction, temperatures of about 120° to 200° C. should beemployed, at CO pressures of at least 500 psig. Addition of high surfacearea activated carbons or zeolites, especially those containing orsupporting platinum or palladium metal, can accelerate cobalt carbonylformation from noncarbonyl precursors. The resulting catalyst ismaintained under a stabilizing atmosphere of carbon monoxide, which alsoprovides protection against exposure to oxygen. The most economical andpreferred catalyst activation and reactivation (of recycled catalyst)method involves preforming the cobalt salt (or derivative) under H₂ /COin the presence of the catalyst promoter employed for hydroformylation.The conversion of Co⁺² to the desired cobalt carbonyl is carried out ata temperature within the range of about 75° to about 200° C., preferablyabout 100° to about 140° C. and a pressure within the range of about1000 to about 5000 psig for a time preferably less than about 3 hours.The preforming step can be carried out in a pressurized preformingreactor or in situ in the hydroformylation reactor.

The amount of cobalt present in the reaction mixture will vary dependingupon the other reaction conditions, but will generally fall within therange of about 001 to about 1 wt %, preferably about 0.05 to about 0.3wt %, based on the weight of the reaction mixture.

The hydroformylation reaction mixture will include a lipophilic phenolto accelerate the reaction rate without imparting hydrophilicity (watersolubility) to the active catalyst. By "lipophilic" is meant that thepromoter tends to remain in the organic phase after extraction of HPAwith water. The phenol will be present in an amount effective to promotethe hydroformylation reaction to HPA, generally an amount within therange of about 0.01 to about 0.6 moles per mole of cobalt.

Suitable phenols include those represented by formula (1): ##STR2## inwhich each R group is independently selected from hydrogen,unsubstituted and non-interfering substituted C₁₋₂₅ linear, branched,cyclic and aromatic hydrocarbyl and mono- and polyalkylene oxide withthe provisos that R₁ and R₅ are not both bulky substituents such ast-butyl and each aromatic ring has no more than one hydroxyl group. Twoor more of the R groups together may form a cyclic or aromatic ringstructure. Such phenols include phenol, nonylphenol, methylphenol,butylphenol, isopropylphenol, bisphenol-A and naphthol.

It is generally preferred to regulate the concentration of water in thehydroformylation reaction mixture, as excessive amounts of water reduce(HPA+PDO) selectivity below acceptable levels and may induce formationof a second liquid phase. At low concentrations, water can assist inpromoting the formation of the desired cobalt carbonyl catalyst species.Acceptable water levels will depend upon the solvent used, with morepolar solvents generally being more tolerant of higher waterconcentrations. For example, optimum water levels for hydroformylationin methyl-t-butyl ether solvent are believed to be within the range ofabout 1 to about 2.5 wt %.

Following the hydroformylation reaction, hydroformylation reactionproduct mixture 4 containing 3-hydroxypropanal, the reaction solvent,1,3-propanediol, the cobalt catalyst and a minor amount of reactionby-products, is cooled and passed to extraction vessel 5, wherein anaqueous liquid, generally water and optional miscibilizing solvent, areadded via 6 for extraction and concentration of the HPA for thesubsequent hydrogenation step. Liquid extraction can be effected by anysuitable means, such as mixer-settlers, packed or trayed extractioncolumns, or rotating disk contactors. Extraction can if desired becarried out in multiple stages. The water-containing hydroformylationreaction product mixture can optionally be passed to a settling tank(not shown) for resolution of the mixture into aqueous and organicphases. The amount of water added to the hydroformylation reactionproduct mixture will generally be such as to provide a water:mixtureratio within the range of about 1:1 to about 1:20, preferably about 1:5to about 1:15. The addition of water at this stage of the reaction mayhave the additional advantage of suppressing formation of undesirableheavy ends. Extraction with a relatively small amount of water providesan aqueous phase which is greater than 20 wt % HPA, preferably greaterthan 35 wt % HPA, permitting economical hydrogenation of the HPA to PDO.The water extraction is preferably carried out at a temperature withinthe range of about 25° to about 55° C. with higher temperatures avoidedto minimize condensation products (heavy ends) and catalystdisproportionation to inactive, water-soluble cobalt species. In orderto maximize catalyst recovery, it is preferred to perform the waterextraction under 50 to 200 psig of carbon monoxide at 25° to 55° C.

The organic phase containing the reaction solvent and the major portionof the cobalt catalyst can be recycled from the extraction vessel to thehydroformylation reaction via 7. Aqueous extract 8 is optionally passedthrough one or more acid ion exchange resin beds 9 for removal of anycobalt catalyst present, arid the decobalted aqueous product mixture 10is passed to hydrogenation vessel 11 and reacted with hydrogen 12 in thepresence of a hydrogenation catalyst to produce a hydrogenation productmixture 13 containing 1,3-propanediol. The hydrogenation step may alsorevert some heavy ends to PDO. The solvent and extractant water 15 canbe recovered by distillation in column 14 and recycled to the waterextraction process, via a further distillation (not shown) forseparation and purge of light ends. PDO-containing stream 16 can bepassed to distillation column 17 for recovery of PDO 18 from heavy ends19.

Hydrogenation of the HPA to PDO can be carried out in aqueous solutionat an elevated temperature during at least a portion of thehydrogenation step of about 40° C., generally within the range of about50° to about 175° C., under a hydrogen pressure of at least about 100psig, generally within the range of about 200 to about 2000 psig. Thereaction is carried out in the presence of a hydrogenation catalyst suchas any of those based upon Group VIII metals, including nickel, cobalt,ruthenium, platinum and palladium, as well as copper, zinc and chromiumand mixtures and alloys thereof. Nickel catalysts, including bulk,supported and fixed-bed forms, provide acceptable activities andselectivities at moderate cost. Highest yields are achieved underslightly acidic reaction conditions.

Commercial operation will require efficient cobalt catalyst recoverywith essentially complete recycle of cobalt to the hydroformylationreaction. The preferred catalyst recovery process involves two steps,beginning with the above-described water extraction of HPA from thehydroformylation product mixture. A majority of the cobalt catalyst willremain in the organic phase, with the remaining cobalt catalyst passinginto the water phase. The organic phase can be recycled to thehydroformylation reactor, with optional purge of heavy ends. Optionally,further decobalting of catalyst in the water layer can be effected bysuitable method, such as complete or partial oxidation of cobaltfollowed by precipitation and filtration, distillation, deposition on asolid support, or extraction using a suitable extractant, preferablyprior to final cobalt removal by ion exchange (9).

The invention process permits the selective and economic synthesis ofPDO at moderate temperatures and pressures without the use of aphosphine ligand for the hydroformylation catalyst. The process involvespreparation of a reaction product mixture dilute in intermediate HPA,then concentration this HPA by water extraction followed byhydrogenation of the aqueous HPA to PDO.

EXAMPLE 1

A 300-ml stirred batch reactor was charged under nitrogen with 0.87 gdicobaltoctacarbonyl, 1.5 g toluene (marker), 2 g deionized water and146 g methyl-t-butyl ether (MTBE). The nitrogen atmosphere was flushedwith H₂, and the reactor was filled to 600 psig H₂ and then to 1200 psigwith 1:1 CO/H₂. Reactor contents were heated to 80° C. for one hour, and10 g of ethylene oxide were then injected, with simultaneous increase inreactor pressure to 1500 psig via addition of 1:1 CO/H₂. Reactorcontents were sampled and analyzed via capillary g.c. (with flameionization detector) at approximately 40% and nearly 100% conversion ofEO, which occurred within two hours. At approximately 40% conversion,3.3 wt % HPA had been formed at a rate of 18 h⁻¹.

EXAMPLE 2

Example 1 was repeated in the absence of added water and with additionof 0.14 g of sodium acetate trihydrate as promoter, added at a ratioNa/Co of 0.2. HPA was formed at a rate of 41 h⁻¹. After cooling andaddition of 30 g deionized water for extraction, only 77% of the cobaltcatalyst remained with the upper solvent layer. 23% of the cobalt wasextracted with the aqueous product. This fraction correspondsapproximately to the amount of sodium acetate added to promote thereaction.

EXAMPLE 3

These experiments illustrate the effectiveness of phenol both toaccelerate the hydroformylation reaction and to permit the recycle ofessentially all the cobalt catalyst in the organic phase following waterextraction of product HPA. Example 1 was repeated with addition of 0.12g of phenol as promoter, for a ratio of 0.25 moles promoter per mole ofcobalt. At approximately 50% conversion, 4.6 wt % HPA had been formed ata rate of 31.4 h⁻¹, or a 74% rate increase over that observed in theabsence of promoter in Example 1. Ultimately, 9.8 wt % HPA was formedbefore termination of the reaction.

Following the reaction, the mixture was cooled to room temperature. 30.6g of deionized water were added for extraction of product under 200 psigsynthesis gas. After 30 minutes, mixing was terminated and 35.55 g of anaqueous product layer containing 25.3 wt % HPA was isolated. The aqueouslayer contained 57 ppm cobalt, or only 1% of the total charged. Theupper organic layer (107.35 g) was analyzed to contain 0.19 wt % cobalt.Recycle of 99% of the cobalt catalyst with the organic layer representsreduction in cobalt loss by a factor of 23, relative to that observedwith sodium acetate promotion in Example 2.

EXAMPLE 4

These experiments illustrate the effectiveness of nonylphenol both toaccelerate the hydroformylation reaction and to permit the recycle ofessentially all the cobalt catalyst in the organic phase following waterextraction of product HPA. Example 1 was repeated with addition of 0.25g of nonylphenol as promoter, for a ratio of 0.2 moles promoter per moleof cobalt. At approximately 50% conversion, 4.5 wt % HPA had been formedat a rate of 32.2 h⁻¹, or a 79% rate increase over that observed in theabsence of promoter in Example 1. The reaction was terminated afterabout 95% conversion of EO, yielding 8.8 wt % HPA.

Following the reaction, the mixture was cooled to room temperature.29.9g of deionized water were added for extraction of product under 200psig synthesis gas. After 30 minutes, mixing was terminated and 34.44 gof an aqueous product layer containing 24.4 wt % HPA were isolated. Theaqueous layer contained 65 ppm cobalt, or only 1% of the total cobaltcharged. The upper solvent layer (113.6 g) was analyzed to contain 0.19%cobalt. Recycle of 99% of the cobalt catalyst with the upper solventlayer represents reduction in cobalt loss by a factor of 23, relative tothat observed with sodium acetate promotion in Example 2.

We claim:
 1. A process for preparing 1,3-propanediol comprising thesteps of:(a) contacting, at a temperature within the range of about 50°to about 100° C. and a pressure within the range of about 500 to about5000 psig, ethylene oxide with carbon monoxide and hydrogen in anessentially non-water-miscible solvent in the presence of an effectiveamount of a non-phosphine ligated cobalt hydroformylation catalyst andan effective amount of a lipophilic phenol promoter under reactionconditions effective to produce an intermediate product mixturecomprising less than 15 wt % 3-hydroxypropanal; (b) adding an aqueousliquid to said intermediate product mixture and extracting into saidaqueous liquid a major portion of the 3-hydroxypropanal at a temperatureless than about 100° C. to provide an aqueous phase comprising3-hydroxypropanal in greater concentration than the concentration of3-hydroxypropanal in the intermediate product mixture, and an organicphase comprising at least a portion of the cobalt catalyst or acobalt-containing derivative thereof and at least a portion of thelipophilic phenol; (c) separating the aqueous phase from the organicphase; (d) contacting the aqueous phase comprising 3-hydroxypropanalwith hydrogen in the presence of a hydrogenation catalyst at a pressureof at least about 100 psig and a temperature during at least a portionof the hydrogenation step of at least about 40° C. to provide ahydrogenation product mixture comprising 1,3-propanediol; (e) recovering1,3-propanediol from the hydrogenation product mixture; and (f)returning at least a portion of the organic phase comprising the cobaltcatalyst or a cobalt-containing derivative thereof and lipophilic phenolto the process of step (a).
 2. The process of claim 1 in which the3-hydroxypropanal in the intermediate product mixture is produced at alevel within the range of about 5 to about 10 wt %.
 3. The process ofclaim 1 in which step (a) is carried out at a temperature within therange of about 60° to about 90° C.
 4. The process of claim 1 in whichstep (b) is carried out under carbon monoxide.
 5. The process of claim 1in which the lipophilic phenol is phenol.
 6. The process of claim 3 inwhich the solvent of step (a) comprises an ether.
 7. The process ofclaim 6 in which the phenol is selected from the group consisting ofphenol and p-alkyl-substituted phenols.
 8. The process of claim 3 inwhich step (a) is carried out at a pressure within the range of about1000 to about 3500 psig.
 9. The process of claim 1 in which the solventof step (a) comprises methyl-t-butyl ether.
 10. The process of claim 9in which step (a) is carried out at a temperature within the range ofabout 75° to about 85° C.
 11. The process of claim 10 in which thelipophilic phenol is phenol.
 12. The process of claim 11 in which thepromoter is present in an amount within the range of about 0.01 to about0.6 moles per mole of cobalt.
 13. The process of claim 1 in which step(c) further comprises removing cobalt compound from the aqueous phase.14. The process of claim 1 in which the H₂ /CO ratio of step (a) iswithin the range of about 1.5:1 to about 5:1.
 15. The process of claim 1in which step (a) is carried out at a rate (TOF) greater than about 30h⁻¹.
 16. A process for preparing 1,3-propanediol comprising the stepsof:(a) reacting, at a temperature within the range of about 60° to about90° C. and a pressure within the range of about 1000 to about 3500 psig,ethylene oxide, carbon monoxide and hydrogen in an essentiallynon-water-miscible solvent comprising methyl-t-butyl ether in thepresence of a catalytic amount of a non-phosphine-ligated cobaltcarbonyl catalyst and about 0.01 to about 0.6 wt % of nonylphenol underreaction conditions effective to produce an intermediate product mixturecomprising 3-hydroxypropanal in a concentration within the range ofabout 5 to about 10 wt %; (b) adding water to said intermediate productmixture in an amount within the range of about 10 to about 25 weightpercent based on the weight of the intermediate product mixture andpermitting the water-containing intermediate product mixture to resolveinto an aqueous phase comprising 3-hydroxypropanal in a concentration ofat least about 20 wt % and an organic phase comprising a major portionof the cobalt catalyst or a cobalt-containing derivative thereof and atleast a portion of the nonylphenol; (c) separating the aqueous phasefrom the organic phase and subsequently removing any cobalt catalystfrom the aqueous phase; (d) contacting the aqueous phase comprising3-hydroxypropanal with hydrogen in the presence of a hydrogenationcatalyst at a pressure of at least about 100 psig and a temperature ofat least about 40° C. to provide a hydrogenation product mixturecomprising 1,3-propanediol; (e) recovering 1,3-propanediol from thehydrogenation product mixture; and (f) returning at least a portion ofthe organic phase comprising cobalt compound and nonylphenol to theprocess of step (a).